Symptoms
- Leak appears soon after installing a new faucet
- Leak at a specific connection point under the sink
- Leak at the base where the faucet meets the sink or counter
- Water runs slightly even with the handle off
Likely causes
- CommonUnder-tightened supply line connectionsNew connections need a firm, snug fit, sometimes more than hand-tight.
- CommonMissing or damaged washer/O-ring at a connectionA part can be pinched, twisted, or left out during assembly.
- PossibleFaucet base not seated flat or missing its gasketCan let water seep out from under the base.
- PossibleCross-threaded fittingThreads that don't engage straight will never seal properly.
What to do
- Turn off the water supply and dry the area completely before testing.
- Turn the water back on and run the faucet, watching closely at each connection point to find the exact source.
- For a loose connection, tighten it firmly with a wrench, checking it isn't cross-threaded first.
- For a leak at the faucet base, confirm the base gasket or plumber's putty was installed per the instructions that came with the faucet.
- If a washer is missing or damaged, disconnect that fitting, install the correct washer, and reconnect.
- Recheck the whole faucet, including the handle area and spout base, once the main leak is fixed.
- Run water for several minutes and check under the sink again before considering the install complete.
Tools and parts
- Adjustable wrench
- Basin wrench
- Plumber's tape
Faucet installation kit / gasketSearch: “faucet mounting gasket kit”
When to call a pro
Call a plumber if you're not confident identifying or reaching the leak point, especially on faucets with tight under-sink clearance.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.